1. Field of the Invention
The present invention relates to an ink-jet recording apparatus. In particular, the present invention relates to an ink-jet recording apparatus which can record a multi-tone image. Further, the present invention relates to an ink-jet recording apparatus in which a driving waveform is applied to non-firing nozzles such that the nozzles do not fire ink thereby.
2. Description of the Related Art
An ink-jet recording apparatus which can be used as an image forming apparatus of a printer, a facsimile machine, a copier or the like is disclosed in Japanese Laid-Open Patent Application No.57-160654, for example. In this ink-jet recording apparatus, variations in diameters of dots can be corrected and/or a multi-tone image can be recorded, as a result of controlling a driving waveform so as to change an ink-firing amount or a dot diameter. In this ink-jet recording apparatus, appropriate pulses are selected from a series of a plurality of voltage pulses, the thus-selected pulses are used for driving an electromechanical transducing device, a plurality of ink drops, the speeds and diameters of which are different from each other, are fired from a nozzle, the thus-fired plurality of ink drops are combined into a single ink drop while the ink drops are flying, the single ink drop hits on a recording medium, and thus, a dot is formed on the recording medium.
Further, Japanese Laid-Open Patent Application No.6-8428 discloses a driving method in which pulse signal outputting means for outputting a plurality of signals, having pulse widths different from each other, in synchronization with a driving signal, and signal selecting means for selecting one signal from the thus-output plurality of signals, are used. Then, the thus-selected signal is used for switching between turning on and turning off of piezoelectric-element driving means during an unsaturated region of the driving signal so that a voltage to be applied to the piezoelectric element is changed. Thus, an amount of an ink drop fired from each nozzle is caused to be fixed.
However, in a recording apparatus such as that disclosed in Japanese Laid-Open Patent Application No.57-160654, in a case where the number of nozzles of an ink-jet head is increased in response to high-integration and high-density in the recording apparatus, because a circuit for selecting pulses is needed for each nozzle, a scale of an entire driving circuit increases, the number of signal wires increases, and the cost therefor increases. Further, a speed of a carriage is increased due to increase in a recording speed, and a period for repetition of dot formation is shortened. As a result, it is difficult to cause successively fired ink drops to be combined to a single ink drop while the ink drops are flying.
Further, in a recording apparatus using a driving method such as that disclosed in Japanese Laid-Open Patent Application 6-8428, because the voltages applied to the piezoelectric elements vary due to variations in transistor-turning-off timings, it is not possible to control the voltages to be applied to the piezoelectric elements in high accuracy. Further, when a driving voltage is controlled, an amount of an ink drop can be increased as a result of increase in the voltage. However, a speed of the ink drop is also increased at the same time. As a result, a point at which the ink drop hits on a recording medium is shifted so that dot-position accuracy is degraded, and/or `satellites` are formed so that image quality is degraded.
Further, in an ink-jet recording apparatus which can be used as an image forming apparatus of a printer, a facsimile machine, a copier or the like, when an ink drop is caused to be fired from a certain nozzle, meniscuses in adjacent nozzles, which are not caused to fire ink drops, respectively (such a nozzle that is not caused to fire an ink drop being referred to as a non-firing nozzle), are in unstable conditions as a result of being affected mechanically or affected by flowing of the ink in the ink-jet head. Thereby, a speed (ink firing speed) Vj of ink fired from the nozzle of the ink-jet head and/or an amount (ink-firing amount) Mj of ink fired from the nozzle of the ink-jet head vary, when each of the adjacent nozzles is then caused to fire an ink drop, and also, a condition in which an ink drop is not fired sufficiently occurs as a result of bubbles being drawn into the nozzle and contained in the ink in the inkjet head.
As a method for eliminating such problems, Japanese Laid-Open Patent Application No.58-62063 discloses a method. In this method, a head in which two pressure-application chambers (ink chambers) are provided so as to face one another is used. In this arrangement, when one pressure-application chamber has pressure applied thereto and thereby an ink drop is fired therefrom, the other pressure-application chamber also has pressure applied thereto but this pressure application is such that an ink drop is not fired thereby.
However, such a method as that disclosed in Japanese Laid-Open Patent Application No.58-62063 can be used only for an ink-jet head having two pressure-application chambers provided so as to face one another.